This invention relates to an improvement of a color picture tube, wherein a set of three electron beams for emitting red, green and blue images, respectively, is emitted from a three-beam in-line type electron gun, and passing through vertically oblong slots of a shadow mask, is led to a black matrix-type screen standing behind the shadow mask so as to energize selectively any of three color-luminous strips which form a set of each three colors on said screen to correspond to said set of three electron color-beams and to produce desired color images.
Apertures of the shadow mask of a color picture tube of this type characterizing the vertically slotted mask as described above are formed in vertically oblong slots. Consequently, as compared with the ordinary-type color picture tubes employing masks having ordinary round apertures, it is already known that this type of tube with slot apertures can select larger areas of apertures for the mask. Accordingly, not only does it reduce electricity wastefully consumed by a portion of electrons striking the mask and failing to pass through it, but also it is able to produce bright pictures on the screen. Besides, it has the advantage of being almost free from color derangement in the vertical direction even in case of thermal expansion of the shadow mask.
However, in the known construction of this type of color picture tube, its screen has a form of massed parallel vertical stripes of red, green and blue luminous strips alternately arranged to emit lights of the respective colors when energized. Furthermore, the light-absorbing film placed in the gaps between the luminous strips for the purpose of improving the contrast serves only to form vertical stripes on the screen. Therefore, it entails a shortcoming in that pictures coming out on the screen are deteriorated by the presence of distinct vertical stripes. On the other hand, slots on the shadow mask have bridging parts between shorter sides of the upper and lower slots, which bridges cause corresponding shadow to be seen as gaps in electron-excited light-irradiating stripes. Such gaps are the parts not excited by the electron beam, and accordingly, do not irradiate light but remain as non-irradiating gray or white parts. The non-irradiating gray or white parts reflect the room light and look white or gray, thereby reducing color purity of the picture.
In order to overcome the abovementioned shortcomings, an invention by Kakuichiro HOSOKOSHI was made and applied for patent by Matsushita Electronics Corporation as follows:
______________________________________ Country Application No. Filing date ______________________________________ USA 475,271 May 31, 1974 (now abandoned) UKGB 26290/74 June 13, 1974 West Germany P24 28 664.4 June 14, 1974 France 74/20947 June 17, 1974 Canada 202,582 June 17, 1974 ______________________________________
In addition, Japanese Pat. application No. 69545/73 was filed on June 18, 1973.
In the abovementioned invention of Kakuichiro HOSOKOSHI, a light absorbing dark film is applied to fill in the gaps between the adjacent shorter sides of phosphor strips, thereby isolating the upper and lower phosphor strips with black gap bands.